The present invention is directed to modified calcium carbonate containing minerals and their use, e.g., in paints and coatings at low dosage, and more particularly to a modified calcium carbonate containing mineral providing a matting effect in paints and coatings, while at the same time providing a smooth paint or coating film.
Today matting effects can be achieved by different means as long as they provide for a micro-roughness of the paint or coating film surface, wherein the incident light is scattered in a way that results in matted surface. The physics behind this is known. The conditions to obtain a perfectly matted effect without resorting to complete light absorption are to scatter the incoming light away from the specular reflectance angle. This means diffracting the directed light that illuminates the substrate causing diffuse scatter.
In paint and coating industries a variety of such matting agents are known and mixed into the paints and coatings such as silica, waxes, organic materials and even fillers are added to form a micro-rough surface after the drying process of the paint or coating. It is recognized as a general rule that the higher the dosing of the matting agent in a paint or coating, the stronger the matting effect. In contrast, products with larger particle sizes are stronger in matting efficiency but the resulting paint or coating film surface is not so smooth. Matting agents with smaller average particle size distribution do not provide sufficient matting effect, but provide for a smoother paint or coating surface.
Japanese patent application JP-A-2003 147275 discloses a coating material composition comprising a binder component and a calcium carbonate treated with phosphoric acid. Said coating material provides for a matte surface providing that the treated calcium carbonate has a mean particle diameter of less than 10 μm, a BET specific surface area of 70-100 m2/g and oil absorption of 130-20 ml/100 g.
WO 2006/105189 A1 refers to aggregated particulate minerals and compositions comprising aggregated calcium carbonate. Said dry aggregated calcium carbonate beads have a weight median aggregate particle size d50 of at least 5 μm and even a size of at least 100 μm. Said aggregated calcium carbonate beads are made into paper, paint, coatings or ceramics.
U.S. Pat. No. 5,634,968 refers to carbonate containing mineral fillers, more particularly for use as matting agents. Said mineral materials are natural and/or precipitated calcium carbonates with a d50 of 9.6-20.5 μm, wherein ground natural calcium carbonates are preferred.
U.S. Pat. Nos. 5,531,821 and 5,584,923 disclose and claim acid resistant calcium carbonates made by mixing calcium carbonate with anionic salts and cationic salts. Said acid resistant calcium carbonate is being used in neutral to weakly acid paper making processes.
U.S. Pat. No. 6,666,953 disclose a pigment of filler containing natural carbonate which is treated with one or more providers of medium-strong to strong H3O+ ions and gaseous CO2.
U.S. 2008/0022901 refers to mineral pigments containing a dry product formed in situ by the multiple reaction between a calcium carbonate and the product or products of reaction of said carbonate with one or more moderately strong to strong H3O+ ion donators and the product or products of reaction of the said calcium carbonate with gaseous CO2 formed in situ and/or originating from an external supply and one or more compounds of formula R-X.
EP 2 264 109 A1 and EP 2 264 108 A1 disclose a process for preparing a surface-reacted calcium carbonate and its use as well as a process to prepare a surface-reacted calcium carbonate implementing the a weak acid, resulting products and uses thereof.